In a display device such as a television using a plasma display panel (hereinafter, it may be referred to as “PDP”.), an optical sheet is disposed on an observer side relative to the PDP. The optical sheet serves to provide the observer with a higher quality image. Therefore, the optical sheet includes prisms which are arranged in parallel along the sheet surface of the optical sheet and transmit therethrough image light from the PDP. Further, the optical sheet includes wedge portions provided between the prisms and suitably blocking or reflecting image light and external light to improve a contrast or to control ghost (see Patent Document 1.).
Patent Document 1: Japanese Patent Application Laid-Open No. 2006-189867